[techtalk] Problems w/Gimp

Laurel Fan lf25+ at andrew.cmu.edu
Sat Nov 20 03:55:24 EST 1999

Excerpts from linuxchix: 20-Nov-99 [techtalk] Problems w/Gimp by Darren
Osadchuk at pangea.c 
> I'm having some odd colour problems with Gimp (and Wordperfect, it turns
> out). When I start Gimp, I get a message which reads, "Unable to allocate
> sufficient colormap entries. Try exiting other color intensive
> applications." The Gimp window then appears in purple (which it shouldn't
> be). Clicking on it will make it turn into the proper grey, but everything
> else on the screen goes wacky. As soon as I move the mouse, everything
> reverts to its normal (screwed up) status. When I start WP, I get the 
> message "Cannot allocate colormap entry for default background" and the
> WP document window is in black and white. Any explanations as to what's
> causing this would be most welcome.

This is because of colormaps (which is one of the more nonintuitive
things about X).  If you're running in 256 color mode (which is usually
the default, another annoying thing), the hardware can only draw 256
different colors.  So that it doesn't draw the same 256 colors every
time, it uses colormaps, which are basically a list of the colors that
it's displaying.  Whenever something wants to use a color, it has to
tell X to put it in its colormap.  If there aren't any left, it'll have
to use one thats already mapped, which is why WP tuns black and white. 
X also allows applicatons to use their own colormaps, and switch them
with X's colormap when they want to.  However, if two programs use
different colormaps, their colors will map differently, so gray in one
will be purple in another, which is what GIMp is doing.  This is
perfectly normal, and longtime X-on-displays-that-can-only-do-256-colors
users have pretty much gotten used to it.

To fix this, either run X with more colors (if you use startx, try
"startx -- -bpp 15", "startx -- -bpp 16" or "startx -- -bpp 24", or even
"startx -- -bpp 32"), or don't use as many color-intensive applications
at a time.

(The numbers are bit depths. bpp stands for bits per pixel.  n bits per
pixel means 2^n (that's an exponent, not an xor, btw) colors, so, 8 bpp
is 2^8=256 colors, 16 bpp is 2^16=64K colors, etc). 

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